CELLULAR ADAPTATION Dr. Mohamed seyam

Cells are able to adapt to changes in work demands or threats to survival by changing their size (atrophy and hypertrophy), Number (hyperplasia), and Form (metaplasia). ■ Normal cellular adaptation occurs in response to an appropriate stimulus and ceases once the need for adaptation has ceased.

Atrophy Decrease in size of a cell or tissue. Decreased size results in decreased oxygen consumption and metabolic needs of the cells and may increase the overall efficiency of cell function. Atrophy is generally a reversible process, except for atrophy caused by loss of nervous innervation to a tissue. Causes of atrophy include prolonged bed rest, disuse of limbs or tissue, poor tissue nutrition and ischemia

PHYSIOLOGIC ATROPHY Some embryonic structures, such as the notochord and thyroglossal duct, undergo atrophy during fetal development. The uterus decreases in size shortly after parturition

PATHOLOGIC ATROPHY Pathologic atrophy: Shrinkage of our brains as we age Disuse atrophy: Essentially when an organ is underused, it undergoes atrophy. Another example of this is an immobilized limb, which undergoes muscle wasting upon casting. Local atrophy: Most often the result of decreased blood flow to that area

Hypertrophy Increase in cell size and tissue mass. Occurs when a cell or tissue is exposed to an increased workload. Occurs in tissues that cannot increase cell number as an adaptive response. The three basic types of hypertrophy are physiologic, compensatory, and pathologic.

Physiologic hypertrophy Physiologic hypertrophy reflects an increase in workload that is not caused by disease — for example, the increase in muscle size caused by hard physical labor or weight training.

Pathologic hypertrophy and Compensatory hypertrophy Pathologic hypertrophy is a response to disease. An example is hypertrophy of the heart muscle as the muscle pumps against increasing resistance in patients with hypertension. Compensatory hypertrophy takes place when cell size increases to take over for non- functioning cells. For instance, one kidney will hypertrophy when the other is not functioning or is removed.

HYPERPLASIA Hyperplasia is an increase in the number of cells caused by increased workload, hormonal stimulation, or decreased tissue density. Increase in the number of cells in an organ or tissue, usually resulting in increased volume of the organ or tissue. Like hypertrophy, hyperplasia may be physiologic, compensatory, or pathologic.

Physiologic hyperplasia Physiologic hyperplasia can be divided into: Hormonal hyperplasia, which increases the functional capacity of a tissue when needed, 1. Proliferation of the glandular epithelium of the female breast at puberty and during pregnancy 2. Occurs in the pregnant uterus. Compensatory hyperplasia, which increases tissue mass after damage or partial resection. 1. Partial hepatectomy --- proliferation of residual liver cells and regeneration of the liver. 2. After unilateral nephrectomy--- when remaining tissue grows to make up for partial tissue loss

PATHOLOGIC HYPERPLASIA Caused by excessive hormonal stimulation or growth factors acting on target cells. Endometrial hyperplasia: Increase in the amount of estrogen. Benign prostatic hyperplasia: Induced by responses to hormones (androgens).

Pathologic metaplasia Pathologic metaplasia is a response to an extrinsic toxin or stressor and is generally irreversible. • For example, after years of exposure to cigarette smoke, stratified squamous epithelial cells replace the normal ciliated columnar epithelial cells of the bronchi. • Although the new cells can better withstand smoke, they don't secrete mucus nor do they have cilia to protect the airway. • If exposure to cigarette smoke continues, the squamous cells can become cancerous.

Dysplasia derangement of cell growth that leads to tissues with cells of varying size, shape and appearance. Generally occurs in response to chronic irritation and inflammation. Common examples include dysplasia of epithelial cells of the cervix or the respiratory tract.

Metaplasia Metaplasia is the replacement of one cell type with another cell type. A common cause of metaplasia is constant irritation or injury that initiates an inflammatory response. Almost exclusively occurs in epithelial cells. Metaplasia may be either physiologic or pathologic. Physiologic metaplasia is a normal response to changing conditions and is generally transient. For example, in the body's normal response to inflammation, monocytes that migrate to inflamed tissues transform into macrophages.

Metaplasia Pathologic metaplasia is a response to an extrinsic toxin or stressor and is generally irreversible. For example, after years of exposure to cigarette smoke, stratified squamous epithelial cells replace the normal ciliated columnar epithelial cells of the bronchi. Although the new cells can better withstand smoke, they don't secrete mucus nor do they have cilia to protect the airway. If exposure to cigarette smoke continues, the squamous cells can become cancerous.

Dysplasia A derangement of cell growth that leads to tissues with cells of varying size, shape and appearance. Generally occurs in response to chronic irritation and inflammation. Common examples include dysplasia of epithelial cells of the cervix or the respiratory tract.

Unit 2 Objectives 1. How do the cells adapt themselves? 2. Define Atrophy? 3. What is the important of atrophy? 4. Give the cause of atrophy? 5. Give the example of physiologic atrophy? 6. Give the example of pathologic atrophy? 7. Define disuse atrophy? 8. Define hypertrophy? In what kind of cell does hypertrophy takes place? 9. Define the different types of hypertrophy with example? 10. Define compensatory hypertrophy? 11. Define hyperplasia and name the types of hyperplasia? 12.Write the division of physiologic hyperplasia?

Unit 2 Objectives 13. Define hormonal hyperplasia? 14. Define compensatory hyperplasia? 15.Write the types of pathologic hyperplasia? 16. Define Metaplasia? 17.Write about physiologic hyperplasia with example? 18.Write about pathologic hyperplasia with example? 19. Pathologic hyperplasia is irreversible? Is this true? 20. Define Dysplasia? 21. Give an example of dysplasia?